GB2063725A - Manufacture of wires for reinforcing rubber articles - Google Patents

Abstract

In the manufacture of steel wires for reinforcing rubber articles, in particular tyres, a layer of zinc is deposited on a brass-coated wire F suitable for wiredrawing in an amount of zinc of between 0.1 and 1 gram per kilogram of steel. The wiredrawing operation to the desired diameter is carried out continuously with the zincing operation. Apparatus for carrying out the process comprises a zincing cell 1 located immediately upstream of a wiredrawing machine 2. <IMAGE>

Description

SPECIFICATION Process for the manufacture of wires for reinforcing rubber articles and a device for use therein The present invention relates to the manufacture of coated steel wires for reinforcing rubber articles, such as tyres, and to a device for use in such manufacture.

Rubber articles are reinforced with steel wires covered with a layer of brass. The main function of the brass is to ensure adequate adhesion between the rubber and the steel, and it also plays an important part during wiredrawing. Brass counting 60% to 75% by weight of copper, the balance being zinc, is generally used.

Studies have shown that in order to have good adhesion with certain types of rubbers, in particular on ageing, it is necessary to use brass which on the surface is richer in zinc.

The zinc gradient can be obtained in various ways, for example by the deposition of alternate layers of copper and zinc on the steel wire, the last layer being zinc, followed by thermal diffusion. If the thermal diffusion is not total, this results in a layer which is richer in zinc on the surface. Another process, which forms the subject of French Patent No. 2,393,856, consists in depositing a thin layer of zinc on the wire covered with a brass of standard composition. After wiredrawing, a brass of non-homogeneous composition is obtained, which is rich in zinc on the surface.

With a treatment of this type, the behaviour of the adhesion on ageing is in fact good.

However, this process had disadvantages. The presence of a layer which is rich in zinc on the surface causes perturbations during wiredrawing. the French Specification states that the optimum deposit of zinc is about 0.06 g per kilogram of wire, and that problems arise during wiredrawing when this deposit exceeds 0.1 g of zinc per kilogram. Nevertheless, the document mentions a level of zinc deposition which can range up to 50 X 10-5 mg per mm2 of application surface, which, for the wire of smallest diameter mentioned in the patent, corresponds to an amount of 0.3 g per kilogram.

Now, complementary experiments have shown that the best adhesion results are only obtained for amounts of zinc of more than 0.1 g/kg and preferably of between 0.3 and 0.7 g/kg. However, in this case, the problems which arise during wiredrawing become very acute and render this operation completely impossible on an industrial scale.

Furthermore, it has been noted, in particular for amounts of zinc of between 0.1 and 0.3 g/kg and amounts above these values, that the wiredrawing problems increase with the length of the period of storage of the wire before drawing. Thus, the difficulties are greater when the wire is drawn, for example, two months after zincing than when it is drawn, for example, on the same day. The explanation which is provided for this phenomenon is that brittle undeformable layers of intermediate phases form on the brass-zinc interface, by diffusion under ambient conditions, and, even at a very low thickness, these layers render the wire unsuitable for drawing under industrial conditions (large number of breakages, significant wear on the die).

This phenomenon is the more pronounced, the thicker is the layer of zinc.

The present invention provides a new process which makes it possible to combine a good ageing resistance of the adhesion with wiredrawing under good industrial conditions. The process of the present invention for the manufacture of a steel wire for reinforcing rubber articles, such as tyres, comprises depositing a layer of zinc on a moving brass-coated steel wire suitable for wiredrawing, in an amount of between 0.1 g and 1 g of zinc per kilogram of steel, and continuously drawing the wire to the desired diameter continuously with the zincing operation. Preferably, the amount of zinc deposited is between 0.1 and 0.6 g/kg of steel.

The zinc is preferably applied by electrolytic deposition during the passage of the wire through a suitable electrolysis bath. It is possible to use any type of bath known in zincing, e.g. a cyanide-based bath, a basic bath without cyanide, an acid bath, or a pyrophosphate bath. Nontoxic baths are preferably used.

The brassing is carried out by the usual methods, namely electrolytic codeposition or brassing by thermal diffusion. A standard brass containing 60% to 75% by weight of copper is used, the amount deposited being between 2 g/kg and 7 g/kg of steel. Optionally, the wire can be cleaned slightly before zincing. The steel is a patented hard steel commonly used for this type of application. The diameter of the wires treated is preferably between 0.80 and 1.90 mm, but can also lie outside these limits. The wiredrawing operation, which takes place continuously with the zincing operation, is carried out under the normal conditions as regards all the parameters (speed, number of passes, number of dies, nature and shape of the dies, lubricant etc.).

Preferably the zinc is deposited while the wire is fed continuously at a speed of 0.3 to 1.3 m/second before drawing and the wire is then drawn, the speed of the drawn wire being 10 to 25 m/second. The time between zincing and drawing is then generally a few seconds to a few tens of seconds.

The process can be carried out using a device, according to the invention, comprising an electrolytic zincing cell located upstream of a wiredrawing machine. Preferably, the zincing cell is controlled so as to run only when the wiredrawing machine is running also. Depending on the control system, the electric current does not flow, on starting, until the wiredrawing machine has reached its normal running speed; the circuit is broken automatically when the wiredrawing machine stops.

Advantageously, direct current is supplied to the zincing cell from the alternating current mains using a rectifier provided with control means to maintain constant the supply of electric current to the zincing cell. This system is advantageous compared with the constant voltage system. In fact, because of the polarisation phenomenon, a deposit forms at the anode and increases the resistance of the circuit. If the voltage is kept constant, the current decreases at the same time as the resistance increases, and the amount deposited, which is proportional to the current, also decreases. The deposit is non-uniform. By maintaining a constant current supply, a uniform deposit, and hence a uniform product, is obtained.

The invention will be understood more clearly with the aid of the Examples below and the figures of the accompanying drawings, in which: Figure 1 schematically shows a device for carrying out the process of the invention; Figure 2 is a graph showing the advantages of the invention; and Figure 3 is a graph of the variation in the composition of the brass, as a function of the depth, for wires treated according to the invention.

The device according to Fig. 1 mainly comprises an electrolytic zincing cell 1 and a wiredrawing machine 2, located downstream, which is shown in part. The zincing cell 1 comprises a tank 3 containing the bath through which the brass-coated wire F passes. The brass-coated wire is fed from a supply reel 4. The bath circulates in a closed circuit from a vat 6, by means of a pump 5. It is fed into the tank 3 through the inlet pipe 7 and it is discharged at both ends of the tank 3 through the pipes 8 and 9, which return it to the vat 6. The anode consists of a basket 10 in which zinc pellets have been deposited, and the wire F is connected to the cathode via the axles of the guide wheels 11 and/or 1 2 located at the inlet and the outlet of the tank 3.

The wire is drawn through the tank by the wiredrawing machine 2. At the outlet of the bath, the zinc-coated wire is rinsed in a tank 14. The wire then passes continuously into the wiredrawing machine 2 of which only two dies 1 5 and two drawing capstans 1 6 have been shown. The wire drawn under the usual conditions is taken up on any suitable support, which is not shown. The device also comprises means, not shown, for bringing the running of the zincing cell under the control of the running of the wiredrawing machine. Depending on these means, the zincing cell does not start up until the wiredrawing machine has reached its normal operating speed. The operation of the zincing cell stops at the same time as that of the wiredrawing machine.The device also comprises means of a known type, which are not shown, for supplying a variable voltage and hence a constant current.

The following examples illustrate the present invention and its advantages. Percentages are by weight.

EXAMPLE 1 This example relates to experiments on the ageing resistance of the adhesion.

The adhesion test is carried out on a wire strand in the following manner: A rubber A is used in order to make calendered webs with the strand to be tested, and these webs are aged for 5 weeks at 21"C and at 65% relative humidity, in a strictly controlled atmosphere. At "zero" time and every week, a sample of the rubber-coated strand is taken and placed in an adhesion test-piece standardised in accordance with U.S. ASTM Standard Specification D 2229-73, the test-piece itself being made of the rubber A. The adhesion is measured by the method of the above standard specification.

The results are reported in Table 1 below and on the graph shown in Fig. 2, on which the ageing time T is plotted on the abscissa and the adhesion, expressed in decanewtons, is plotted on the ordinate.

la Control The control consists of a strand of the 4 x 0.25 S 12.5 type, that is to say consisting of 4 wires each of diameter 0.25 mm, twisted in the S direction with a pitch of 1 2.5 mm. The wire of diameter 0.25 mm is obtained by drawing a wire of diamter 1.25 mm, made of patented hard steel. Before wiredrawing, the wire of diameter 1.25 mm has been coated with a layer of brass at a rate of 5.8 g of brass per kilogram of steel wire, the brass containing 66% of copper and 34% of zinc. After wiredrawing, a brass-coated wire of diameter 0.25 mm is obtained, which comprises 5 g/kg of brass containing 65.8% of copper and 34.2% of zinc.

The loss of 0.8% by weight of brass is a normal loss which is frequently observed in wiredrawing. Starting from this wire, a 4 X 0.25 S 1 2.5 strand is thus manufactured and the adhesion test is carried out on this strand.

The results are reported in Table 1 below and on the graph according to Fig. 2: curve A.

1b The above adhesion test is carried out on a strand produced from a 1 sot wire treated according to the invention. The starting wire is identical to that of Example la, that is to say a wire of diameter 1.25 mm, coated with a brass containing 66% of copper and 34% of zinc, at a rate of 5.8 g of brass per kilogram of steel wire. Subsequently, in accordance with the present invention, zinc is applied to the brass at a rate of 0.1 5 g of zinc per kilogram of steel wire. This gives a wire which, before entering the wiredrawing machine, comprises 5.95 g of coating per kilogram of steel wire, the coating having an average composition of 64.5% of copper and 35.5% of zinc. The wire is drawn continuously with the zincing operation, under the conditions of the invention.This gives a thin wire of diameter 0.25 mm, coated with 4.8 g/kg of a brass having an overall composition of 65% of copper and 35% of zinc. Starting from this wire, a 4 X 0.25 S 1.25 strand is manufactured as in Example la and the same adhesion test is applied to this strand. The results are reported in Table 1 and on the graph according to Fig. 2 curve B. A distinct improvement in the ageing resistance is already observed.

ic The above adhesion test is carried out on a strand produced from a second wire according to the invention.

The starting wire is identical to that of Examples la and ib. Subsequently, a zincing operation is carried out in accordance with the present invention, the amount of zinc being 0.5 g/kg of steel wire. This gives a wire which, before entering the wiredrawing machine, comprises an amount of coating of 6.3 g/kg, the overall composition of the coating being 60.5% of copper and 39.5% of zinc. The wire is drawn continuously with the zincing operation, under the conditions of the invention. After wiredrawing, a thin wire of diameter 0.25 mm is obtained, which is coated with 5.6 g/kg of a brass having an overall composition of 62% of copper.

Starting from this thin wire, a 4 X 0.25 S 1 2.5 strand is manufactured as in Examples la and ib and the adhesion test is applied. The results are reported in Table 1 and on the graph according to Fig. 2 : curve C. A significant improvement in the ageing resistance of the adhesion is observed.

TABLE 1 Example Adhesion in decanewtons, daN Time 0 1 week 2 weeks 3 weeks 4 weeks 5 weeks la control 38 21.2 18.2 16.2 17.3 17 1b 37 28.3 26.8 24.2 23.8 21.2 1c 36 32.8 31 30.8 30.4 30.6 The periods in these examples correspond to periods of storage of the calendered webs before manufacture of the tyres. It is observed that the improvement in the ageing resistance of the adhesion increases with the amount of zinc applied to the surface.

The zinc applied to the surface, before wiredrawing, mixes partially with the brass during wiredrawing because of mechanical phenomena and phenomena of partial thermal diffusion.

This gives a finished wire covered with a brass of non-homogeneous composition which is richer in zinc on the surface, as shown by surface analyses carried out by ESCA photoelectron spectroscopy (Electron Spectroscopy for Chemical Analysis).

The graph according to Fig. 3 gives, as a function of the depth ("peeling depth"), the value of the percentage of copper atoms, measured from intensity peaks corresponding to the 2p3/2 electron energy levels. The analysis relates to three wires, namely the control wire according to Example la and wires according to Examples ib and ic. The following observations are made: in general, for the three wires, the composition of the brass changes according to the depth: the copper content increases with the depth and then remains virtually constant beyond about 500 , and for the wires treated according to the invention, the brass is poorer in copper on the surface: by comparison with the above adhesion results, this confirms that the ageing resistance of the adhesion increases with the content of zinc on the surface.

EXAMPLE 2 The purpose of this Example is to demonstrate the fact that the suitability of the wire for drawing is not affected by the zinc coating if, according to the invention, the wiredrawing operation is carried out continuously with the zincing operation.

2a The control wire is the brass-coated wire of diameter 1.25 mm, according to Example la, which is subjected to wiredrawing under the usual conditions in order to obtain a wire of final diameter 0.25 mm. The test consists in measuring, in kilometres, the length of wire drawn before it is necessary to change the dies, taking account of the usual tolerances in the diameter of the finished wire. For the control wire, the length in kilometres is expressed by a base number of 1 00.

2b The treated wire is the wire according to Example ib, that is to say the wire according to la, coated with 0.15 g/kg of zinc. It is drawn continuously with the zincing operation, under identical conditions to the control wire 2a. The length drawn before changing the dies is 1 20, relative to the base of 100.

2c The wire treated is the wire according to Example ic, that is to say the wire according to la coated with 0.5 g/kg of zinc. It is drawn continuously with the zincing operation, under identical conditions to the control wire 2a. The length drawn before changing the dies is 95, relative to the base of 100.

2d The wire used has been subjected to a treatment of the type known according to French Patent 2,393,856. The starting wire is the brass-coated wire according to Example 7a, coated with 0.35 g/kg of zinc. After zincing, the wire is stored for 1 5 days and then drawn under the same conditions as the control wire 2a. The length drawn before changing the dies is 5 to 10, relative to the base of 100. Moreover, it is observed that the wire is very non-uniform and that breakages are frequent. Wiredrawing under industrial conditions cannot be carried out.

Example 2 shows that, in contrast to the known processes, there are no particular wiredrawing difficulties and there is no increase in the difficulties in accordance with the amount of zinc deposited on the surface if, according to the invention, the wiredrawing operation is carried out continuously with the zincing operation. On the other hand, if wiredrawing is carried out discontinuously, as in the prior art, great wiredrawing difficulties are encountered, which increase in accordance with the amount of zinc deposited and with the length of the intermediate storage period.

Examples 1 and 2, taken together, clearly demonstrate the advantages of the invention, namely: there is no difficulty, during wiredrawing, for zinc deposits ranging up to 1 g/kg of steel, and the ageing resistance of the adhesion is distinctly improved, relative to the prior art, by virtue of thicker zinc deposits of up t 1 g/kg of steel.

EXAMPLE 3 The purpose of this Example is to demonstrate the improvement in the ageing resistance of the adhesion.

The test is carried out in the following manner: A rubber B is used to manufacture a caiendered web with the wire to be tested. Test-pieces are manufactured, each of which is produced by cutting two pieces from the said web and placing them on top of one another to intersect at 90 . The test-pieces are aged in a climatic oven at 35"C and 98% relative humidity in order to reproduce conditions of storage in a tropical climate. The test-pieces are aged respectively for zero, 3, 6, 9 and 1 5 days, after which they are vulcanised. After vulcanisation, the two pieces of web are torn apart and a score of zero to five is awarded as a function of the rubber covering adhering to the wires, five corresponding to maximum covering and zero to no covering.

(a) The control wire is obtained from a steel wire of diameter 1.25 mm, coated with brass containing 65% of copper, at a rate of 4.7 g/kg. This wire is drawn to a diameter of 0.25 mm under the usual conditions. This gives a wire of diameter 0.25 mm, coated with a brass containing 64.5% of copper, at a rate of 4 g/kg. A 4 X 0.25 S 12.5 strand is produced from this wire as in the above examples, and it is subjected to the above test; the following results are obtained: TABLE 2 Days 0 3 6 9 15 Score 5 3 1 0 0 (b) A wire manufactured by the process according to the invention is then subjected to the test. The starting wire is a brass-coated steel wire of diameter of 1.25 mm, the amount of brass is 4.5 g/kg and its composition is 69.5% of copper and 31.5% of zinc. This brass-coated wire is treated with zinc at a rate of 0.4 g of zinc per kilogram of steel. This gives a wire which, after zincing and before entering the wiredrawing machine, comprises an amount of brass of 4.9 g/kg, the brass containing 63.8% of copper overall. The zinc-coated wire is drawn continuously according to the invention. After wiredrawing, a brass-coated wire of final diameter 0.25 mm is obtained, the amount of brass being 4.1 g/kg and its overall composition being 65% of copper and 35% of zinc. This wire is twisted to form a 4 X 0.25 S 1 2.5 strand, which is subjected to the test described above; the following results are obtained: TABLE 3 Days 0 3 6 9 15 Score 5 5 5 5 4 A very significant increase in the ageing resistance of the adhesion is noted with the wire manufactured by the process according to the invention.

EXAMPLE 4 The purpose of this Example is also to demonstrate the ageing resistance of the adhesion. It involves an ageing test in an autoclave, in the presence of moisture, at 1 20 C, for 8 hours and under a pressure of about 2 bars. The adhesion is measured in accordance with ASTM Standard Specification D 2229-73 on test-pieces produced with a rubber C.

The controls consist of two strands, namely 4 X 0.25 S 12.5 and 5 X 0.25 S 9.5 strands, of which the wires were obtained by drawing a brass-coated steel wire of diameter 1.25 mm. The tests are carried out on strands having an identical structure to that of the controls consisting of wires obtained by the same process as the wires of the controls, the difference being the application of the zincing operation according to the invention.

The results are reported in the following table (Table 4), in which: the "structure" column shows the conformation of the strands, the "brass:wire BZ" column relates to the brass-coated wire Before Zincing and gives the amount of brass deposited, in g/kg, relative to the steel, and the percentage of copper in this brass, the "addition of Zn" column gives the amount of zinc deposited, in g/kg, relative to the steel, in the case of wires according to the present invention, the "brass:wire BW" column gives the amount of brass after zincing and Before Wiredrawing, and the overall percentage of copper in this brass, the "brass::strand" column gives the amount of brass remaining after wiredrawing, and the overall percentage of copper in this brass, and in the "adhesion" column, the adhesion being measured in accordance with ASTM Standard Specification D 2229-73, Ao denotes the initial adhesion, before passage through the autoclave, and Aa denotes the adhesion after 8 hours in the autoclave, expressed in daN.

TABLE 4 Brass:wire BZ Brass:wire BW Experiment ------------ Addition No. Structure g/kg % Cu of ZN g/kg % Cu 41 5.6 66.5 0 5.6 66.5 control 42 5 X 0.25 S 9.5 5.3 69.4 0.35 5.65 65 43 4.2 68.8 0.35 4.55 63.5 44 4.8 67.5 0 4.8 67.5 control -- 4 x 0.25 S 12.5 45 4.2 68.8 0.35 4.55 63.6 Brass:strand Adhesion Experiment No. g/kg %CU Ao Aa 41 4.5 65.7 47.0 18.0 42 5.1 67 53.5 33.5 43 3.6 65.2 50.0 34.5 44 3.9 68 40.5 13 45 3.9 65.5 43.5 25 The figures given in this Table show: For the first control strand 41, a significant drop is observed between the initial adhesion and the adhesion after passage through the autoclave.

For the strand 42, produced from wires treated according to the invention, it is observed that, although the adhesion at time zero is of the same order as for the strand 41, the drop in the adhesion on ageing, on the other hand, is much smaller. The same remarks can be made for the strand 45 in comparison with the control 44.

A small drop in the adhesion is also observed for the strand 43.

The above Examples clearly demonstrate the advantages of the invention, which makes it possible to have an improved ageing resistance of the adhesion, relative to the known processes, together with a good suitability for wiredrawing.

The invention can be applied to steel wires for reinforcing rubber articles, in particular for reinforcing tyres.

Claims (11)

1. Process for the manufacture of a steel wire for reinforcing rubber articles, such as tyres, which comprises depositing a layer of zinc on a moving brass-coated steel wire suitable for wiredrawing in an amount of between 0.1 and 1 gram of zinc per kilogram of steel and continuously drawing the wire to the desired diameter.

2. Process according to Claim 1, in which the amount of zinc deposited is between 0.1 and 0.6 gram per kilogram of steel.

3. Process according to Claim 1 or 2, in which the zinc is applied by electrolytic deposition.

4. Process according to any one of Claims 1 to 3, in which the layer of zinc is applied to a brass-coated wire in which the amount of brass is between 2 grams and 7 grams per kilogram of steel.

5. Process according to Claim 4 in which the brass contains 60 to 75% by weight of copper and 40 to 25% by weight of zinc.

6. Process according to any one of Claims 1 to 5 in which the steel wire has before coating a diameter of 0.80 to 1.90 mm.

7. Process according to any one of Claims 1 to 6 in which the zinc is deposited while the wire is fed continuously at a speed of 0.3 to 1.3 m/second before drawing, and the wire is then drawn, the speed of the drawn wire being 10 to 25 m/second.

8. Process according to Claim 1 substantially as described in any one of the Examples 1 b, ic, 2b, 2c, 3b, and Example 4, experiments 42, 43, or 45.

9. Brass-coated steel wire produced by the process of any of the preceding Claims.

10. Device for carrying out the process according to one of Claims 1 to 9, comprising an electrolytic zincing cell located upstream of a wiredrawing machine.

11. Device according to claim 10, in which the zincing cell is controlled so as to run only when the wiredrawing machine is running also.

1 2. Device according to claim 11, in which current control means are provided to maintain constant the supply of electric current to the zincing cell.

1 3. Device according to Claim 10 substantially as described with reference to Fig. 1 of the accompanying drawings.